1. Field of the Invention
The invention relates to an electrochemical single battery such as fuel cells, and so forth, and, more particularly, it is concerned with such electrochemical single battery having an increased reaction area so as to augment its output density, and a method for producing such electrochemical single battery.
2. Discussion of Background
In the following, explanations will be given on the electrochemical single battery, taking a fuel cell as an example.
As has already been well known, the fuel cell is a kind of electric generating device, from which electric energy is taken out. The construction of this fuel cell is such that an electrolyte layer holding therein an electrolyte is interposed between a fuel electrode and an oxidizer electrode, both being arranged in a mutually opposed relationship, and a fuel and an oxidizer are fed into the fuel electrode and the oxidizer electrode, respectively, to thereby take out the electric energy therefrom.
Depending on the kind of the electrolyte used, the fuel cell is classified into various types such as an alkali type, a phosphoric acid type, a high molecular weight solid electrolyte type, a molten carbonate type, a solid electrolyte type, and others.
Hereinbelow, explanations will be given on the phosphoric acid type fuel cell as an example. The most common structure of the phosphoric acid type fuel cells is the so-called "rib-separator type", the typical cell structure of which is described in U.S. Pat. No. 3,867,206 (Japanese Patent Publication No. 152/1983) and U.S. Pat. No. 4,276,355 (Japanese Unexamined Patent Publication No. 66067/1984).
FIG. 13 of the accompanying drawing shows a cross-sectional view of a typical structure of the "rib-separator type" fuel cell. The fuel cell is constructed with an electrolyte layer 1 to hold therein an electrolyte; a fuel electrode 2 which is made up of an electrode base material 3 and a reaction (catalyst) layer 4; an oxidizer electrode 5 which is made up of an electrode base material 6 and a reaction (catalyst) layer 7; gas separation plates 10 (also called separators, or bi-polar plates, or inter-connectors); oxidizer gas flow passages 11, and fuel gas flow passages 12. The cell is called "rib-separator type", because these gas flow passages 11 and 12 are formed in the gas separator plate 10. In another way, a structure, in which the gas flow passages are formed in the electrodes, is also feasible.
In the following, the electrochemical reaction in the fuel cell will be explained. In the reaction (catalyst) layer 4 of the fuel electrode 2, hydrogen as fed through the reaction gas flow passages 12 discharges the electrons to be turned into the hydrogen ions, as follows. EQU H.sub.2 .fwdarw.2H.sup.+ +2e.sup.-
The hydrogen ions move in and through the electrolyte held in the electrolyte layer 1 towards the reaction (catalyst) layer 7 of the oxidizer electrode 5. In the reaction (catalyst) layer 7 of the oxidizer electrode 5, the hydrogen ions, the electrons which have been produced in the reaction (catalyst) layer 4 of the fuel electrode 2 and have flown through an external circuit, and oxygen which has been fed through the reaction gas flow passages 11 are reacted to produce water, as follows. EQU 1/20.sub.2 +2H.sup.+ +2e.sup.- .fwdarw.H.sub.2 O
As a whole, these two reactions can be expressed in the following manner, whereby electric generation is effected in the form of electrons flowing through the external circuit. EQU H.sub.2 +1/20.sub.2 .fwdarw.H.sub.2 O
In such fuel cell, the reaction (catalyst) layer has the same area as that of a single battery surface. As the consequence of this, it was not possible to increase an output density of the fuel cell per unit area.
In this connection, the inventors of the present application previously proposed to augment the reaction area by corrugating the surface of the reaction (catalyst) layer (vide: Japanese Unexamined Patent Publications No. 217955/1984, No. 29453/1988 and No. 29454/1988). FIG. 14 of the accompanying drawing shows a cross-sectional view of one example of such corrugated layer surface, by which the area of the reaction section has increased from L.sub.1 to L.sub.2.
On the other hand, in the fuel cell or the like, the reaction (catalyst) layer should have its tight gas-sealing property on its outer peripheral part, for the purpose of which the present inventors also proposed previously to improve such gas-sealing property of the fuel cell (vide: Japanese Unexamined Patent Publications No. 193065/1987, No. 16565/1988 and No. 181266/1988).
In the conventional electrochemical single battery as mentioned above, it is required that the electrode base material be provided in advance with such corrugation for the purpose of imparting such corrugated form to the reaction (catalyst) layer, which therefore inevitably complicated the cell structure, and necessitated precise machining only to increase its manufacturing cost, and other problems.
On the other hand, at the gas-sealed peripheral part, it is necessary to fill a sealing material in the electrode base material, or to arrange fresh sealing material within one and the same plane of the electrode, with the consequent problems such that the cell structure becomes complicated, stepped parts tend to occur in the cell structure, and so forth.